Pneumatic Compression fittings, Poly-Tite is a line of brass compression fittings that is furnished pre-assembled, ready for installation. Poly-Tite nuts will rotate around the sleeve as it tightens preventing twisting and weakening of the plastic tube. Poly-Tite fittings have a machined in tube support and can be used with most thermoplastic tubing. A brass sleeve is available for use with soft metal and nylon tubing.